1. Field of the Invention
The present invention relates to a code division multiple access (CDMA) type mobile communication terminal, and more particularly to an apparatus for stabilizing a transmission power of a CDMA mobile communication terminal.
2. Description of the Related Art
In case of a CDMA type mobile communication terminal, the dynamic range of a transmission section is wide, and thus it is very difficult to implement a transmission power stabilizing circuit. This is because a transmission power detector does not have the dynamic range of about 90 dB that is required in the CDMA mobile communication terminal.
Generally, the transmission power stabilization implemented in the CDMA mobile communication terminal is performed in two ways. First is a method whereby an automatic gain controller reads an output of the transmission power detector for a period of 1.25 m, and reflects this on the transmission power. Since this method cannot perform the power stabilization when it is actually implemented, a compensation method using an average value in an RAS (Radio Frequency Analog Subsystem) table is employed. However, this compensation method using the average value in the RAS table has problems in that it greatly suffers from variations of power, cannot perform an accurate compensation according to deviations in temperature and frequency, and has a large load on a radio frequency task. Further, it can be applied only for a transmission power of about −20 dBm due to the limited dynamic range of the transmission power detector.
Second is a method that monitors in real time the output of the transmission power detector, and if the transmission power is varied from a determined power, returns the transmission power to the determined power by adjusting the gain of an automatic gain control amplifier through a feedback loop. Since this method enables a real-time process, the power stability becomes high with a rapid response. However, it also has problems in that it can be applied only for a transmission power of about −20 dBm due to the limited dynamic range of the transmission power detector.
Since the above-described two power stabilizing methods are applicable only in a state that the data rate of the transmission signal is maximum, it is difficult to apply the methods to the CDMA mobile communication terminal whose data rate is frequently changed, and thus whose detected power is also changed.